Formative Assessment

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During the guided instruction portion of the lab, listen
carefully to student responses as they brainstorm potential physical
properties. Guide students to use everyday experience with water to
form proper conclusions regarding water’s properties.

The Physical Properties Lab provides an opportunity to assess
students’ understanding of the guided instruction. During the lab,
rotate between student teams and use the following questions as a
guide in determining student understanding:

“You determined the mass and
volume of Unknown 1. Do you think mass and volume are physical
properties? Why or why not?”

“If you increased the amount of
Unknown 1, would the density change? Why or why not?”

“If you were to smell Unknown 2,
is that a function of how well it evaporates? Why or why not?”

“What are some other physical
property tests you could perform to aid in identifying the
unknowns?”

Suggested Instructional Supports

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The lesson focuses on describing matter based on physical
properties. Students may be familiar with several of the properties
listed; however, this lesson provides a detailed definition as well
as demonstration of each property. Students are evaluated based on
their involvement and responses during the demonstrations as well as
on the lab.

The lesson’s demonstrations allow students to experience
physical properties first-hand and relate them to their daily life.
They can relate what they saw during the demonstrations to the
questions of the lab.

The demonstrations give students experiences that they can
apply to more complex situations. For example, as you demonstrate
the density of CO2 being greater than that of air,
students should relate that fact to fire extinguishers, even though
the connection may not be explicitly mentioned during class.

Some students may benefit from helping with or even
conducting a demonstration. The teacher may ask students to write
down a hypothesis based on previous knowledge before they perform
the demonstration. An extension for students who may be going beyond
the standards is provided as well.

The lesson is organized so that students are taught basic
definitions first and then apply them to an experiment. They are
able to interact with the teacher and their classmates during these
demonstrations, which culminate in the summary lab and lab
questions. The lesson’s material is then applied throughout the
remaining lessons.

Instructional Procedures

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Fill a large glass with water even to the
rim. Ask students, “Is this glass of water full? How many paper
clips do you think I could add to this glass of water, before the
water overflows?” Students will see that you can add many more
paper clips to the glass than they thought.

Follow this demonstration with another quick
example:

Give a penny, pipette, and a small jar
of water to every fourth student.

Have groups of four (at their desks)
first estimate how many drops of water the surface of the penny will
hold before the water spills over the sides, and then perform the
experiment.

Have students place the penny on the
desk and begin to place as many drops of water as they can on the
coin until water runs off the surface of the penny.

For an extension, students could try this
same demonstration with isopropyl alcohol or an alkane, such as
hexane, instead of water.

Part 1

Ask students, “Why do you think you can
add several more paper clips to the already full glass of water? Why
could you add more drops of water to the penny than you could with
alcohol or hexane?” Let students make educated guesses. Some
may offer answers such as, the water is denser or it sticks together
more. Tell them, “All of the substances that we looked have
unique physical properties. The physical property you just explored
is called surface tension, which allowed the water molecules to cling
to the side of the glass and the penny.”

Let this answer guide you into a discussion
of physical properties. Put the definition of physical properties on
the board, overhead or interactive white board. Working with water,
ask students to brainstorm other physical properties of water. On the
board, make a list of their answers. When you feel that they have
exhausted their guesses, circle the ones that are correct and then
add properties that were not yet guessed. Define each. Below is a
list of some physical properties. You may add to or remove from the
list any properties you want.

Density: Density is a physical property that describes how
much mass is in a specific volume. D = m/v.

Conductivity: Describes how well something conducts
electricity.

Magnetism: Describes how matter responds to a magnetic field.

Boiling/Melting/Freezing Point: The temperature at which a
substance boils/melts/freezes.

Thermal Expansion/Contraction: Describes the change in volume
as a substance is heated or cooled.

Malleability: How easily a substance can be molded, bent, and
shaped.

Ductility: the extent to which a material can be deformed
plastically without fracturing.

Surface Tension: The cohesive forces between liquid
molecules.

Volatility: A measure of the tendency of a substance to
evaporate.

Part 2

Demonstrate some of water’s physical
properties.

Demonstration 1(Boiling Point)

Set up a distillation apparatus on the front counter. Add tap
water and food coloring to the round bottom flask. Let the water
distill for a few minutes. Explain that distillation “is a
method of physically separating a mixture based on the boiling
points of the components in the mixture. The mixture is made from
water and food coloring. Water has a specific boiling point (at a
given pressure), which is 100ºC. Food coloring has a higher boiling
point than water. You will see the water boil first, vaporize into a
gas, and then condense back into liquid water (because of the cool
water running around the outermost channel). Eventually, you will be
left with just dye in the round bottom flask and pure water in the
beaker.” If you do not have access to a distillation
apparatus, you can show students a distillation animation, such as
this one:
http://www.saskschools.ca/curr_content/science10/unita/redon18.html

Demonstration 2 (Thermal Contraction/Expansion)

Ask students, “Has anyone left a can of soda in the freezer
or in a cold car too long?” Most students have had experience
with this and will acknowledge that the can exploded. Then ask, “Of
what is soda mainly made?” Students might say sugar, bubbles,
and water. Focus on water, which is over 90% of soda’s volume.
“Soda is mainly water, which, unlike most liquids, expands when
it freezes! This is a physical property of water, called thermal
expansion.”

If you have access to liquid nitrogen, you
could fill a balloon with helium and place it in the liquid nitrogen
to see that helium contracts when it is cooled, unlike water. If you
do not have access to liquid nitrogen, you could demonstrate the same
thing by placing the balloon in the freezer for about an hour.

Demonstration 3 (Density)

Introduce this next physical property with a glass of ice water
sitting on the front table. Ask students what they notice about the
glass. Lead them to thinking about why the ice cubes are floating on
the liquid water. Remind them that the solid ice and liquid water
are the same thing, just in different states. Explain, “Solid
water is less dense than liquid water. As water freezes, it expands,
creating more volume. Since density is a function of volume, solid
water is less dense. Less dense substances will float!” Do a
follow up demonstration using isopropyl alcohol (rubbing alcohol).
Fill a graduated cylinder with the alcohol and place ice cubes in
the cylinder. The ice will sink because it has a greater density
than isopropyl alcohol.

In a clear tank (an empty aquarium would
work) place several liters of water. In front of students, place a
can of cola and a can of diet
cola into the tank. Explain, “There is considerably more
mass per unit volume in the regular cola than the diet cola, causing
it to be denser and sink.”

Demonstration 4 (Conductivity)

Place a sample of distilled water that you purchased from the
store (or use the distilled water from Demonstration 1)in a
beaker. Use a conductivity set with a light bulb to show that
distilled water is a poor conductor of electricity. Do the same with
salt water, which will be a better conductor.

Demonstration 5 (Viscosity)

Pour a small amount of honey from a high height (so students can
see) into a jar. Do the same with water. Ask, “which substance
has a higher viscosity, remembering that viscosity is resistance to
flow?”

For students performing above and beyond the standards,
consider discussing fractional distillation, used in the petroleum
industry. For details and an animation of this process, go to:
http://www.howstuffworks.com/oil-refining4.htm

If you have access to dry ice (CO2), you can place
about 3 cups of it in an aquarium. Let it sublimate for 10 to 15
minutes. Light a candle. Take a beaker and “scoop” out some of
the CO2 vapor. It will look to students as if you are not
removing anything. Quickly pour the vapor over the burning candle.
The flame will extinguish due to the density of CO2.
Relate this to fire extinguishers.

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